The present invention relates to a tape cassette provided with a brake member for locking undue rotation of hubs in an inoperative condition of the tape cassette.
As a tape cassette for carrying out high-density recording of a video signal or a PCM signal, such as 1/2-inch video tape cassette or 8-mm video tape cassette, there have been practically used various kinds of tape cassettes including a brake member for nonrotatably locking hubs in order to prevent slacking of a magnetic tape in an inoperative (storage) condition of the tape cassettes.
In the inoperative condition of the tape cassettes, such a brake member is biased by a biasing force of a spring to come into pressure contact with the hubs and thereby nonrotatably lock the hubs. In an operative condition of the tape cassettes, the brake member is moved away from the hubs by a lock release pin to be inserted from the outside of a cassette case, thereby releasing the locked condition of the hubs.
FIGS. 1A, 1B, 2A and 2B illustrate the operation of such a brake member, wherein FIGS. 1A and 2A show operational conditions as viewed in plan, and FIGS. 1B and 2B show the operational conditions as viewed in side elevation. In these figures, reference numeral 63 denotes a cassette case of a tape cassette, which is shown by a one-dot chain line. The cassette case 63 accommodates a brake member 61, a pair of reel hubs 62, and a magnetic tape T wound around the reel hubs 62.
The brake member 61 is provided with a pair of engaging pawls 61a adapted to contact engaging teeth 62a like gear rings formed on the reel hubs 62 and thereby lock the rotation of the reel hubs 62. A brake spring 61c formed from a stainless steel wire is fixed to a pair of spring holding portions 61b of the brake member 61. In a normal (inoperative) condition of the tape cassette, the brake spring 61c is in pressure contact with an abutment portion 64 provided in the cassette case 63. Accordingly, a biasing force of the brake spring 61c is normally applied to the brake member 61 in such a direction as to engage the engaging pawls 61a of the brake member 61 with the engaging teeth 62a of the reel hubs 62, thereby maintaining a locked condition of the reel hubs 62 as shown in FIGS. 1A and 1B.
On the other hand, when the tape cassette is loaded into a tape player, a lock release pin 65 provided in the tape player is inserted from an insertion hole 63a formed through the cassette case 63 as shown in FIG. 2B. As a result, the lock release pin 65 comes into contact with an inclined cam portion 61d of the brake member 61 located in opposition to the insertion hole 63a, and urges the brake member 61 against the biasing force of the brake spring 61c, with the result that the engagement of the engaging pawls 61a of the brake member 61 with the engaging teeth 62a of the reel hubs 62 is released to thereby bring the reel hubs 62 into a rotatable condition as shown in FIG. 2A.
Reference numeral 63b shown by a one-dot chain line denotes a window portion formed through an upper half of the cassette case 63. Although not shown, a similar window portion is also formed through a lower half of the cassette case 63. These window portions 63b are molded from transparent resin. By the provision of the window portions 63b, a residual quantity of the magnetic tape T may be confirmed from the outside of the cassette case 63. The brake member 61 is provided with an aperture 61e at a position corresponding to the window portions 63b, so that the residual quantity of the magnetic tape T may be confirmed from the window portion 63b on the side of the brake member 61 through the aperture 61e.
The brake member 61 is further provided with a guide hole 61f for guiding sliding movement of the brake member 61 from the hub locked condition to the hub unlocked condition. A guide pin 66 fixed in the cassette case 63 is inserted in the guide hole 61f.
FIGS. 3A, 3B, 3C, and 3D are a top plan view of the brake member 61 in the prior art by way of example, a cross section taken along the line A--A in FIG. 3A, a bottom plan view of the brake member 61 shown in FIG. 3A, and an elevational view of the brake member 61 shown in FIG. 3A, respectively.
As mentioned above, the sliding movement of the brake member 61 for the hub locking operation and the hub unlocking operation is effected primarily by the cooperation of the engaging pawls 61a, the spring holding portions 61b, the brake spring 61c formed from a stainless steel wire or the like, and the inclined cam portion 61d. The entirety of the brake member 61 except the brake spring 61c is molded from engineering plastics (mainly, POM) in consideration of a wear resistance to the lock release pin 65 (normally, metal such as SUS) in the tape player and a sliding property with respect to an inner surface of the cassette case 63. As shown in FIGS. 3A to 3D, the brake spring 61c is supported at its opposite ends by the spring holding portions 61b in such a manner that the opposite ends are nipped by the spring holding portions 61b each of which is formed in a zigzag shape.
However, in the conventional brake member 61 having the brake spring 61c merely supported at its opposite ends, the brake spring 61c is slidable in an axial direction thereof, causing possible disconnection of the brake spring 61c in the axial direction from the spring holding portions 61b. Accordingly, there arise the problems of reduction in workability in installation of the brake member and reduction in reliability in the braking operation.
As apparent from FIGS. 1B and 2B, a portion of the brake member 61 except the inclined cam portion 61d must be accommodated between the magnetic tape T and the inner surface of the cassette case 63. Thus, a thickness of the portion of the brake member 61 except the inclined cam portion 61d is greatly limited. For example, in a micro tape cassette for recording a PCM signal which has been recently developed, the adoption of the brake member 61 requires that the thickness of the portion of the brake member 61 except the inclined cam portion 61d is to be set to about 0.4 mm or less. Accordingly, a thickness of the spring holding portions 61b is also limited in accordance with this set value. However, if the spring holding portions 61b are formed by molding, a minimum thickness of the spring holding portions 61b is about 0.4 mm, and this thickness is hard to reduce.
Accordingly, even if the brake spring 61c formed from a stainless steel wire having a very small diameter of about 0.2 mm, for example, is intended to be supported or fixed by insert molding to the spring holding portions 61b, the fixing itself of the brake spring 61c is difficult or it is difficult to securely fix the brake spring 61c because there is no room in the thickness direction of the spring holding portions 61b.
Further, as mentioned above, the brake member 61 is provided with the aperture 61e so as not to hinder the confirmation of a residual quantity of the magnetic tape T from the window portions 63b of the cassette case 63. By the provision of the aperture 61e, a central portion of the brake member 61 is almost occupied by the aperture 61e, and a sufficient rigidity of side portions 61g formed on opposite sides of the aperture 61e cannot be obtained. As mentioned above, the brake member 61 is slidably moved in the same direction as that of flexing of the brake spring 61c to be effected by the cooperation of the lock release pin 65 with the inclined cam portion 61d. Accordingly, if the rigidity of the side portions 61g is insufficient, they are apt to be flexed in a thickness direction thereof, causing a deterioration in braking operation. Moreover, when the side portions 61g are flexed, they come into contact with the magnetic tape T wound around the reel hubs 62, causing an increase in loss torque and a deterioration in tape running. In this manner, a reduction in the rigidity of the brake member 61 is greatly undesirable.
Further, if the window portions of the cassette case 63 are larger in size than the window portions 63b as shown, the size of the aperture 61e of the brake member 61 must also be increased. In this case, as a sufficient space for forming the guide hole 61f does not remain in the brake member 61, it is obliged that a guide recess 61f' continuing to the aperture 61e as shown in FIG. 4 is to be formed in the brake member 61. That is, the guide recess 61f' is opened at one end thereof to the aperture 61e, and the guide pin 66 is adapted to be inserted through the guide recess 61f'.
In the hub locked condition, the guide pin 66 is located at a position 66a relative to the guide recess 61f', and in the hub unlocked condition, the guide pin 66 is located at a position 66b relative to the guide recess 61f'. Thus, in the hub unlocked condition, the guide pin 66 is located outside the guide recess 61f'. It is therefore necessary to accurately introduce the guide pin 66 into the guide recess 61f' in bringing the brake member 61 into the hub locked condition again.
However, if the brake member 61 is slipped in position even a little upon unlocking the hubs, it cannot be expected that the guide pin 66 is smoothly introduced into the guide recess 61f' by the sliding movement of the brake member 61 in locking the hubs again. In many cases, the guide pin 66 comes against a periphery of the opened one end of the guide recess 61f', thus hindering the sliding movement of the brake member 61. As a matter of course, a proper hub locking operation cannot be exhibited.